In slicing wafers from silicon, etc., bars or rods for use in, for example, the electronics, optical or photovoltaic industry, two principal costs are the cost of the material or ingot itself, and the cost (including material yield) of cutting the ingot into wafers. It is desirable to decrease the latter by minimizing the amount of material lost during cutting, and maximizing cutting speed and blade life.
In the past, wafer yield has been increased by using blades in which abrasive particles are attached (typically by plating) on only the cutting edges. Blade life has been improved by reducing abrasive particle pullout. These improvements are discussed in U.S. Pat. Nos. 4,187,828 and 4,384,564, both assigned to the assignee of this application.
However, kerf loss remains significant. When, for example, the desired wafer thickness is about 300 .mu.m, it has proved difficult to achieve better than about 60% material utilization; and a wide kerf width also results in reduced cutting speed. Conventional rectangular in cross-section blades require abrasive that extends well beyond the sides of the blade to provide the necessary relief. Circular cross-section blades require less relief, but tend to wander and twist and their smaller cross-section also limits the feed force that may be employed. For example, slicing tests using the Fixed Abrasive Slicing Technique (FAST; see F. Schmid, M. B. Smith and C. Khattak in Proceedings of 23rd Photovoltaic Specialists Conference, in Louisville, Ky., USA, May 1993, p. 205) showed that reduction of wire size below 200 .mu.m diameter caused excessive wander due to reduction of tension forces resulting from decreasing cross-sectional area, and that 200 .mu.m wire, plated with 45 .mu.m diamond abrasive, resulted in an approximately 300 .mu.m kerf.